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Although the information contained in this Code has been obtained from sources believed to be reliable, New Zealand Metal Roofing Manufacturers Inc. makes no warranties or representations of any kind (express or implied) regarding the accuracy, adequacy, currency or completeness of the information, or that it is suitable for the intended use.

Compliance with this Code does not guarantee immunity from breach of any statutory requirements, the New Zealand Building Code or relevant Standards. The final responsibility for the correct design and specification rests with the designer and for its satisfactory execution with the contractor.

While most data have been compiled from case histories, trade experience and testing, small changes in the environment can produce marked differences in performance. The decision to use a particular material, and in what manner, is made at your own risk. The use of a particular material and method may, therefore, need to be modified to its intended end use and environment.

New Zealand Metal Roofing Manufacturers Inc., its directors, officers or employees shall not be responsible for any direct, indirect or special loss or damage arising from, as a consequence of, use of or reliance upon any information contained in this Code.

New Zealand Metal Roofing Manufacturers Inc. expressly disclaims any liability which is based on or arises out of the information or any errors, omissions or misstatements.

If reprinted, reproduced or used in any form, the New Zealand Metal Roofing Manufacturers Inc. (NZMRM) should be acknowledged as the source of information.

You should always refer to the current online Code of Practicefor the most recent updates on information contained in this Code.


This Code of Practice provides requirements, information and guidelines, to the Building Consent Authorities, the Building Certifier, Specifier, Designer, Licensed Building Practitioner, Trade Trainee, Installer and the end user on the design, installation, performance, and transportation of all metal roof and wall cladding used in New Zealand.

The calculations and the details contained in this Code of Practice provide a means of complying with the performance provisions of the NZBC and the requirements of the Health and Safety at Work Act 2015.

The scope of this document includes all buildings covered by NZS 3604, AS/NZS 1170 and those designed and built under specific engineering design.

It has been written and compiled from proven performance and cites a standard of acceptable practice agreed between manufacturers and roofing contractors.

The drawings and requirements contained in this Code illustrate acceptable trade practice, but recommended or better trade practice is also quoted as being a preferred alternative.

Because the environment and wind categories vary throughout New Zealand, acceptable trade practice must be altered accordingly; in severe environments and high wind design load categories, the requirements of the NZBC will only be met by using specific detailing as described in this Code.

The purpose of this Code of Practice is to present both Acceptable Trade Practice and Recommended Trade Practice, in a user-friendly format to ensure that the roof and wall cladding, flashings, drainage accessories, and fastenings will:

  • comply with the requirements of B1, B2, E1 E2 and E3 of the NZBC;
  • comply with the design loading requirements of AS/NZS 1170 and NZS 3604 and with AS/NZS 1562;
  • have and optimised lifespan; and
  • be weathertight.

COP v24.03:Durability; Tray-Roofing-Clip-Durability

4.17 Tray Roofing Clip Durability 

As a rule, a fastener should be no less durable than the material it is fastening. With secret fixed fasteners over a benign internal environment, this is easily achieved.

The potential for air-borne salt ingress into the cavity of a tray roof is low; the pan is flat or nearly flat, the ribs are narrow and closed at the ends. The BRANZ publication, Research Now: Roof Ventilation 2, tested the durability of metals inside a vented and unvented ceiling space. Even in this Extreme Marine environment, the corrosion rate was low. Their conclusion was that the installation of ventilation openings to roof cavities should not have a negative effect on the long-term performance of galvanised metal fixtures in these spaces.  In the unvented spaces, the corrosion rate was even lower.

Compatibility of materials should also be considered. Aluminium, zinc, and aluminium/zinc alloys are compatible in contact. While not normally considered compatible, stainless steel clips have also been proven to be durable, and not affect the durability performance of aluminium, zinc, aluminium/zinc alloys, or copper, in a dry internal environment.

Over wet and corrosive internal environments, or where the underside of a roof or canopy is exposed to weather from underneath, both the durability of the clip and compatibility of the roof and cladding material must be assessed in accordance with the micro-environment.

In all cases, adequate ventilation of the roof or wall is essential to prevent degradation of the cladding and other building elements.


4.17A Allowable Clip Material for Tray and Trough Cladding Over Dry Internal Environments

Pre-painted SteelPre-painted aluminiumZincCopper


Stainless steel,

Painted galvanised,
stainless steel,
Stainless steel,
stainless steel,